Pick-and-place system with a stabilizer

ABSTRACT

A pick-and-place system is provided. The pick-and-place system includes: a wafer holder configured to hold a bottom die; a gantry having a stabilizer extending downwardly; a primary drive mechanism connected to the gantry and configured to drive the gantry horizontally and vertically; a suction head configured to hold a top die; and a secondary drive mechanism located at the gantry and connected to the suction head and configured to drive the suction head horizontally and vertically to place the top die on the bottom die at a target position. The primary drive mechanism drives the gantry vertically until the stabilizer is in contact with the bottom die before the secondary drive mechanism drives the suction head.

FIELD

Embodiments of the present disclosure relate generally to semiconductorpackaging, and more particularly to a pick-and-place system used forsemiconductor packaging.

BACKGROUND

In recent years, the semiconductor industry has experienced rapid growthdue to continuous improvement in the integration density of a variety ofelectronic components (e.g., transistors, diodes, resistors, capacitors,etc.). For the most part, improvement in integration density hasresulted from iterative reduction of minimum feature size, which allowsmore components to be integrated into a given area.

These continuously scaled electronic components require smaller packagesthat occupy less area than previous packages. Exemplary types ofpackages include quad flat pack (QFP), pin grid array (PGA), ball gridarray (BGA), flip chips (FC), three-dimensional integrated circuits (3DICs), wafer-level packages (WLPs), and package on package (PoP) devices.For instance, the front-end, 3D IC stacking technologies are used forre-integration of chiplets partitioned from System on Chip (SoC). Theresulting integrated chip outperforms the original SoC in systemperformance. It also affords the flexibility to integrate additionalsystem functionalities. Advantages of those advanced packagingtechnologies like 3D IC stacking technologies include improvedintegration density, faster speeds, and higher bandwidth because of thedecreased length of interconnects between the stacked chips. However,there are quite a few challenges to be handled for the technologies ofadvanced packaging.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a schematic diagram illustrating an example pick-and-placesystem in accordance with some embodiments.

FIG. 2 is a flowchart illustrating an example method for bonding a topdie to a bottom die using the pick-and-place system shown in FIG. 1 inaccordance with some embodiments.

FIGS. 3A-3E are schematic diagrams illustrating a portion of thepick-and-place system at various stages in accordance with someembodiments.

FIG. 4A is a top view of an example alignment pattern in accordance withsome embodiments.

FIG. 4B is a perspective view of a stabilizer landing foot that isaligned with the alignment pattern shown in FIG. 4A in accordance withsome embodiments.

FIG. 5 is a side view of an example bottom die having alignment patternsnd stabilizer landing feet in accordance with some embodiments.

FIG. 6 is a top view of an example alignment pattern in accordance withsome embodiments.

FIG. 7 is a top view of an example alignment pattern in accordance withsome embodiments.

FIG. 8 is a top view of an example alignment pattern in accordance withsome embodiments.

FIG. 9 is a top view of an example target contact area in accordancewith some embodiments.

FIG. 10 is a top view of an example alignment pattern in accordance withsome embodiments.

FIG. 11 is a diagram illustrating the functioning of an example opticsalignment system in accordance with some embodiments.

FIG. 12 is a diagram illustrating the functioning of another exampleoptics alignment system in accordance with some embodiments.

FIG. 13 is a schematic diagram illustrating an example pick-and-placesystem in accordance with some embodiments.

DETAILED DESCRIPTION OF THE INVENTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the subject matterprovided. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Some embodiments of the disclosure are described. Additional operationscan be provided before, during, and/or after the stages described inthese embodiments. Some of the stages that are described can be replacedor eliminated for different embodiments. Some of the features describedbelow can be replaced or eliminated and additional features can be addedfor different embodiments. Although some embodiments are discussed withoperations performed in a particular order, these operations may beperformed in another logical order.

Packaging technologies were once considered just back-end processes,almost an inconvenience. Times have changed. Computing workloads haveevolved more over the past decade than perhaps the previous fourdecades. Cloud computing, big data analytics, artificial intelligence(AI), neural network training, AI inferencing, mobile computing onadvanced smartphones, and even self-driving cars are all pushing thecomputing envelope. Modern workloads have brought packaging technologiesto the forefront of innovation, and they are critical to a product'sperformance, function, and cost. These modern workloads have pushed theproduct design to embrace a more holistic approach for optimization atthe system level.

Stacking chiplets, or modular dies, with multi-layers, multi-chip sizes,and multi-functions is at the heart of advanced packaging technologies.Among other technologies, hybrid bonding (HB) is key component ofstacking chiplets. Hybrid bonding is a process that stacks and bondsdies using both dielectric bonding layers and metal-to-metalinterconnects in advanced packaging. Hybrid bonding can provide improvedintegration density, faster speeds, and higher bandwidth. Hybrid bondingcan be used for wafer-to-wafer bonding, die-to-wafer bonding, anddie-to-die bonding.

For die-to-wafer boding and die-to-die boding, which involve stacking adie on a wafer, a die on an interposer, or a die on a die, theinfrastructure to handle dies without particle adders, as well as theability to bond dies, becomes a major challenge. Typically, back-endprocesses, such as dicing, die handling, and die transport on filmframe, have to be adapted to front-end clean levels, allowing highbonding yields on a die level. For example, copper hybrid bonding isconducted in a cleanroom in a wafer fab, instead of in an outsourcedsemiconductor assembly and test (OSAT) facility.

Pick-and-place systems are part of the infrastructure to handle dies inthe context of die-to-wafer boding and die-to-die boding. Apick-and-place system is an automatic system that can pick a die (oftenreferred to as a “top die”) and place it onto another die (oftenreferred to as a “bottom die”) or a host wafer, often in a high-speedmanner. A person may take the complexity and difficulty of such tasks ofpicking and placing a top die for granted. On the contrary, accuratealignment of dies, without comprising the high system throughput, isvery challenging, especially considering that the alignment accuraciesare on the order of microns (i.e., micrometers). If the position shifterror cannot be further reduced, the critical size of hybrid bondingmetal pads cannot be reduced, which in turn limits bonding density.Among other things, one particular challenge comes from the fact thatthe moving parts, especially a suction head, in a pick-and-place systemthat handle the top die may be shaky and unsteady, subject to variousvibrations resulting from various sources in the system. As a result,the position shift error is hard to reduce.

In accordance with some aspects of the disclosure, a pick-and-placesystem and a method for operating a pick-and-place system are provided.The pick-and-place system has a gantry driven by a primary drivemechanism. A secondary drive mechanism is located at the gantry anddrives a suction head to place a top die on a bottom die to achieve, forexample, hybrid bonding of the top die and the bottom die. The gantryhas a stabilizer extending downwardly. In one example, the stabilizerincludes four legs. The primary drive mechanism drives the gantryvertically until the stabilizer is in contact with the bottom die. Avision alignment camera is used in this process to facilitate thealignment. In some embodiments, there are alignment patterns on thebottom die to be used for the alignment. Subsequently, the secondarydrive mechanism drives the suction head such that the top die is placedon the bottom die at a target position. Due to the existence of thestabilizer, the movement of the suction head becomes more steady,thereby reducing the position shift error. In some implementations, anoptics alignment system monitors the position of the suction head, andan alignment feedback is generated based on the position of the suctionhead. The secondary drive mechanism then drives the suction head basedon the alignment feedback. As such, an alignment feedback loop isachieved using the optics alignment system. The system and methoddisclosed are generally applicable to various use cases such asdie-to-die bonding, die-to-wafer bonding, and the like.

FIG. 1 is a schematic diagram illustrating an example pick-and-placesystem 100 in accordance with some embodiments. In the example shown inFIG. 1 , the pick-and-place system 100 includes a wafer holder 102, aprimary drive mechanism 110, an attaching shaft 112, a gantry 114, asecondary drive mechanism 116, a stabilizer 118, a suction head 120, asuction shaft 130, a vision alignment camera 126, an optics alignmentsystem 128, a vacuum device 132, a control unit 170, a vision alignmentprocessor 172, a memory device 174, a display 176, and an I/O device178. It should be understood that more or fewer components than thoseshown in FIG. 1 can be employed in other examples. In the example shownin FIG. 1 , the pick-and-place system 100 can pick a top die 106,typically coming from a component wafer after a dicing process, andplace the top die 106 on a bottom die 104.

The wafer holder 102 is used to hold a wafer or a die. In the exampleshown in FIG. 1 , the bottom die 104 is placed on the wafer holder 102in a die-to-die bonding context. In other examples, a host wafer can beplaced on the wafer holder 102 in a die-to-wafer bonding context. Itshould be understood that although the bottom die 104 is used as anexample throughout the description, the disclosed technologies are alsoapplicable to bonding the top die 106 to a host wafer, in which casethere are multiple bottom dies on the host wafer.

In the example shown in FIG. 1 , the bottom die 104 has a front side(denoted as “F” in FIG. 1 ) and a back side (denoted as “B” in FIG. 1 ).In the example shown in FIG. 1 , the bottom die 104 has been flipped,i.e., upside down. A bonding layer 156 is formed at the back side and ona silicon substrate 150. In one implementation, the bonding layer 156 ismade of a dielectric and can be used for bonding with another bondinglayer 156 at the top die 106.

One or more semiconductor devices (e.g., transistors, resistors,capacitors, inductors, etc.) are formed on the silicon substrate 150,before being flipped, in a front-end-of-line (FEOL) process. Amultilayer interconnect (MLI) structure 152 is disposed over the one ormore semiconductor devices, before being flipped. The MLI structure 152includes a combination of dielectric layers and conductive layersconfigured to form various interconnect structures. The conductivelayers are configured to form vertical interconnect features (e.g.,device-level contacts, vias, etc.) and horizontal interconnect features(e.g., conductive lines extending in a horizontal plane). Verticalinterconnect features typically connect horizontal interconnect featuresin different layers (e.g., a first metal layer often denoted as “Ml” anda fifth metal layer often denoted as “M5”) of the MLI structure 152.During operation of bottom die 104, the interconnect structures areconfigured to route signals and/or distribute signals (e.g., clocksignals, voltage signals, ground signals) to the one or moresemiconductor devices to fulfill certain functions. It should beunderstood that although the MLI structure 152 is depicted in FIG. 1with a given number of dielectric layers and conductive layers, thepresent disclosure contemplates MLI structures having more or fewerdielectric layers and/or conductive layers depending on designrequirements of the bottom die 104.

In the example shown in FIG. 1 , the bottom die 104 includes a hybridbonding metal pad 158 formed in the bonding layer 156, and the hybridbonding metal pad 158 is connected to the MLI structure 152 through athrough-silicon via (TSV) 154, which penetrates the silicon substrate150 in a vertical direction (i.e., a Z-direction). It should beunderstood that although only one hybrid bonding metal pad 158 and a TSV154 is shown in FIG. 1 , this is not intended to be limiting.

Likewise, the top die 106 has a front side (denoted as “F” in FIG. 1 )and a back side (denoted as “B” in FIG. 1 ). In the example shown inFIG. 1 , the top die 106 has been flipped, i.e., upside down. Thesilicon substrate 150 of the top die 106 is held (e.g., sucked) to andin contact with the suction head 120, details of which will be describedbelow. A bonding layer 156 is formed at the front side and over a MLIstructure 152, before the top die 106 is flipped. In one implementation,the bonding layer 156 is made of a dielectric and can be used forbonding with the bonding layer 156 at the bottom die 104, as mentionedabove. Likewise, the top die 106 includes a hybrid bonding metal pad 158formed in the bonding layer 156, and the hybrid bonding metal pad 158 isconnected to the MLI structure 152 through, for example, a via. Itshould be understood that although only one hybrid bonding metal pad 158and a TSV 154 are shown in FIG. 1 , this is not intended to be limiting.

The top die 106 is picked by the suction head 122, and then thepick-and-place system 100 controls the suction head 120 accordingly tomove the top die 106 to a target position, for example, right over thebottom die 104. Subsequently, the suction head 120 places the top die106 onto the bottom die 104. The top die 106 and the bottom die 104 arebonded because of the bonding layers 158 on each side, in someimplementations at room temperatures. In the meantime, the hybridbonding metal pads 158 on each side are in contact with each other,forming an electrical connection path between the top die 106 and thebottom die 104.

The primary drive mechanism 110 and the gantry 114 are connected throughthe attaching shaft 112. The primary drive mechanism 110 can drive thegantry 114 both in the vertical direction (i.e., the Z-direction) and inthe horizontal plane (i.e., the X-Y plane, that is in the X-directionand/or the Y-direction). In one implementation, the primary drivemechanism 110 is an actuator, a rail, a continuous track, a steppermotor, gears, belts, or a combination thereof. It should be understoodthat this is not intended to be limiting, and other implementations ofthe primary drive mechanism 110 are within the scope of the disclosure.

The gantry 114 and the suction head 120 are connected through thesuction shaft 130. A secondary drive mechanism 116 is located at thegantry 114 and can drive the suction head 120 both in the verticaldirection (i.e., the Z-direction) and in the horizontal plane (i.e., theX-Y plane, that is in the X-direction and/or the Y-direction). In oneimplementation, the secondary drive mechanism 116 is an actuator, astepper motor, or a combination thereof. In another implementation, thesecondary drive mechanism 116 drives the suction head 120 by usingmagnetic forces. It should be understood that this is not intended to belimiting, and other implementations of the secondary drive mechanism 116are within the scope of the disclosure.

The gantry 114 has a stabilizer 118. In one implementation, thestabilizer 118 includes multiple legs extending downwardly from thegantry 114 in the Z-direction. In one example, the stabilizer 118includes four legs. In another example, the stabilizer 118 includesthree legs. It should be understood that these examples are not intendedto be limiting, and any leg number that is equal to or larger than threeis within the scope of the disclosure, since three points can determinea plane. In one implementation, the stabilizer 118 is made of metal. Thestabilizer 118 is in contact with the top surface of the bottom die 104first, under the control of the primary drive mechanism 110, and thenthe second drive mechanism 116 controls the suction head 120 to placethe top die 106 on the bottom die 104 at the target position. Becausethe stabilizer 118 is in contact with the top surface of the bottom die104 first, the suction head 120 becomes more steady when it approachesthe bottom die 104 to place the top die 106, thereby reducing theposition shift error. It should be understood that various featuresshown in FIG. 1 are not drawn to scale. For instance, the relativedimensions of the gantry 114, the stabilizer 118, the suction head 120,the top die 106, and the bottom die 104, the wafer holder 102 may bedifferent than those shown in FIG. 1 .

A vision alignment camera 126 is located at the gantry 114. The visionalignment camera 126 is a downward camera that can detect the exactposition of the gantry 114, and more specifically, the position of thestabilizer landing feet 138, relative to the bottom die 104. A visionalignment processor 172 is utilized to assist the primary drivemechanism 110 in driving the gantry 114 to a target gantry position. Insome embodiments, some alignment patterns 136 can be formed on thebottom die 104. Each of the alignment patterns 136 corresponds to eachof the stabilizer landing feet 138, and the vision alignment processor172 and the vision alignment camera 126 can utilize the alignmentpatterns 136 to adjust the position of the gantry 114 accordingly toachieve an accurate landing of the stabilizer 118.

The vacuum device 132 is connected to the suction shaft 130 through apipe 134. The suction shaft 130 is hollow and has a passage in themiddle that extends in the Z-direction. When the vacuum device 132operates, the suction head 120 generates a suction force to hold the topdie 106 to a bonder region 122. The suction head 120 also includes anauxiliary region 124, which accommodates an optics alignment system 128.The optics alignment system 128 is configured to assist the suction head120 to adjust its position accordingly and place the top die 106 at thetarget position, with the help of a control unit 170.

Details of the operations of the primary drive mechanism 110, thesecondary drive mechanism 116, the vision alignment camera 126, thealignment pattern 136, and the optics alignment system 128 will bedescribed below with reference to FIGS. 2-12 .

The control unit 170 is configured to execute computer program codesstored in the memory device 174 in order to cause the pick-and-placesystem 100 to fulfill its various functions. In some implementations,the control unit 170 is a controller, a central processing unit (CPU), amulti-processor, a distributed processing system, an applicationspecific integrated circuit (ASIC), and/or a suitable processing unit.It should be understood that the vision alignment processor 172 can be aportion of the control unit 170 in some embodiments.

The memory device 174 is configured to store computer program codes thatare executed by the control unit 170 and other information needed forfulfilling various functions of the pick-and-place system 100. In someimplementations, the memory device includes one or more of asemiconductor or solid-state memory, a magnetic tape, a removablecomputer diskette, a random access memory (RAM), a read-only memory(ROM), a rigid magnetic disk, and/or an optical disk. It should beunderstood that other types of memory devices can be employed as well.

In the example shown in FIG. 1 , the pick-and-place system 100 furtherincludes various input/output (I/O) device 178, including a display 176.An operator can input instructions through the input devices such as amouse, a keyboard, a voice control input device, and the like. Theoutput devices such as the display 176 can present the status of thepick-and-place system 100, the progress of its tasks, and the like, tothe operator.

FIG. 2 is a flowchart illustrating an example method 200 for bonding atop die to a bottom die using the pick-and-place system 100 shown inFIG. 1 in accordance with some embodiments. In the example shown in FIG.2 , the method 200 includes operations 202, 204, 206, 208, and 210.Additional operations may be performed. Also, it should be understoodthat the sequence of the various operations discussed above withreference to FIG. 2 is provided for illustrative purposes, and as such,other embodiments may utilize different sequences. These varioussequences of operations are to be included within the scope ofembodiments. FIGS. 3A-3E are schematic diagrams illustrating a portionof the pick-and-place system 100 at various stages in accordance withsome embodiments.

At operation 202, the suction head 120 picks the top die 106. In someimplementations, the top die 106 comes from a component wafer after thecomponent wafer has been diced using, for example, a blade or laserstealth dicing system. As explained above, the suction head 120 can pickthe top die 106 using a suction force generated by the vacuum device132, and the top die 106 is stuck to the bonder region 122. In someimplementations, the top die 106 is selected, ejected from the componentwafer using an ejector, picked up and flipped using a flipper if needed,and transferred to the suction head 120. In some embodiments, anup-looking camera is used to determine the exact position of the top die106 on the suction head 120.

As shown in the example in FIG. 3A, the suction head 120 has picked thetop die 106, but the top die 106 is not over the bottom die 104 at thetarget position where the hybrid bonding metal pads 158 are aligned inthe X-Y plane.

The method 200 then proceeds to operation 204, where the primary drivemechanism 110 drives the gantry 114 horizontally above the bottom die104. In one implementation, the vision alignment camera 126, which is adown-looking camera, can generate a vision. The vision alignmentprocessor 172 can determine the location of the gantry 114 based on thevision. In one embodiment, the alignment patterns 136 on the bottom die104 can be used as the benchmark to determine the location of the gantry114 relative to the bottom die 104. Once the location of the gantry 114relative to the bottom die 104 is known, the vision alignment processor172 can calculate the distances in the X-direction and the Y-direction,respectively, that the gantry 114 should move. In one example, theprimary drive mechanism 110 is a stepper motor, and the stepper motorreceives instructions to move the calculated distances in theX-direction and the Y-direction, respectively.

As shown in the example in FIG. 3B, the primary drive mechanism 110 hasmoved the gantry 114 above the bottom die 104, and the legs of thestabilizer 118 are preliminarily aligned with the correspondingalignment patterns in the X-Y plane. Since the primary drive mechanism110 has its own movement resolution, which is typically not as fine asthat of the secondary drive mechanism 116, the alignment is coarse,without any comprise in the speed of the movement.

The method 200 then proceeds to operation 206, where the primary drivemechanism 110 drives the gantry 114 vertically to a predetermined height(denoted as “h” in FIG. 3C) at a first speed (denoted as “v1” in FIG.3C). In the example shown in FIG. 3C, the predetermined height h ismeasured from the top surface of the bottom die 104 to the bottom of thestabilizer landing feet 138. In one embodiment, the predetermined heighth is equal to or larger than 0.01 mm. In another embodiment, thepredetermined height h is between 0.1 cm and 0.5 cm.

As shown in the example in FIG. 3B, after the vertical movement of thegantry 114, the stabilizer landing feet 138 are approaching the topsurface of the bottom die 104, and the legs of the stabilizer 118 arestill roughly aligned with the alignment patterns 136. It should beunderstood that the primary drive mechanism 110 can adjust the positionof the gantry 114 in the X-Y plane using the vision alignment camera 126and the vision alignment processor 172 during and/or after operation206. It should be understood that in some embodiments, operations 204and 206 can be carried out at the same time, and the vision alignmentcamera 126 and the vision alignment processor 172 can be employed foralignment in some embodiments.

The method 200 then proceeds to operation 208, where the secondary drivemechanism 116 drives the gantry 114 vertically at a second speed(denoted as “v2” in FIG. 3C) until the stabilizer 118 (specifically, thestabilizer landing feet 138) is in contact with the bottom die 104. Insome implementations, the second speed v2 is slower than the first speedv1. As such, the touchdown of the stabilizer 118 (specifically, thestabilizer landing feet 138) is gentle, preventing it from moving ordamaging the bottom die 104. In the example shown in FIG. 3D, thestabilizer landing feet 138 are in contact with the top surface of thebottom die 104 and aligned with the alignment patterns 136 in the X-Yplane. Likewise, it should be understood that the primary drivemechanism 110 can adjust the position of the gantry 114 in the X-Y planeusing the vision alignment camera 126 and the vision alignment processor172 during operation 208. Details of the alignment patterns 136 will bedescribed below with reference to FIGS. 4A-10 .

The method 200 then proceeds to operation 210, where the secondary drivemechanism 116 drives the suction head 120 such that the top die 106 isplaced on the bottom die 104 at the target position. In oneimplementation, operation 210 can include operations 212, 214, and 216,where an alignment feedback loop is achieved using the optics alignmentsystem 128. At operation 212, the optics alignment system 128 monitorsthe position of the suction head 120 relative to the bottom die 106. Insome implementations, the optics alignment system 128 includes a lightemitter and a light receiver, and the position of the suction head 120can be calculated based on the received light after reflection,refraction, diffraction, or the combination thereof. In one example, theposition is calculated by a processor inside the optics alignment system128 located at the auxiliary region 124 of the suction head 120. Inanother example, the position is calculated by either the visionalignment processor 172 or the control unit 170 shown in FIG. 1 .Details of monitoring the position of the suction head 120 using theoptics alignment system 128 will be described below with reference toFIGS. 11-12 .

At operation 214, an alignment feedback is generated based on theposition of the suction head 120. Since both the position of the suctionhead 120 and the target position are known, an alignment feedback can begenerated to fine-tune a position offset. For instance, the positionoffset is a microns in the X-direction and -b microns in theY-direction. Since the secondary drive mechanism 116 has a movementresolution that is higher than that of the primary drive mechanism 110,the position offset can have a high resolution, which enables thefine-tuning of the position of the suction head 120. Likewise, in oneexample, the alignment feedback is generated by a processor inside theoptics alignment system 128 located at the auxiliary region 124 of thesuction head 120. In another example, the alignment feedback isgenerated by either the vision alignment processor 172 or the controlunit 170 shown in FIG. 1 .

At operation 216, the secondary drive mechanism 116 drives the suctionhead 120 based on the alignment feedback. In one implementation, thesecondary drive mechanism 116 receive instructions from the control unitshown in FIG. 1 to drive the suction head both in the X-Y plane,according to the alignment feedback, and in the Z-direction.

In the example shown in FIG. 3E, the top die 106 has been placed on thebottom die 104 at the target position. The bonding layers 156 on thebottom die 104 and the top die 106 are in contact with each other, andthe bottom die 104 and the top die 106 are bonded together, for example,at room temperatures. On the other hand, the hybrid bonding metal pads158 are aligned in the X-Y plane and in contact with each other, formingan electrical connection between the bottom die 104 and the top die 106.It should be understood that although the examples shown in FIGS. 1 and3A-3E are related to hybrid bonding, the method 200 shown in FIG. 2 isnot limited to those examples. That is, the method 200 shown in FIG. 2is applicable to other contexts that a top die is placed on a bottom dieusing a pick-and-place system.

FIG. 4A is a top view of an example alignment pattern 136 a inaccordance with some embodiments. FIG. 4B is a perspective view of astabilizer landing foot 138 a that is aligned with the alignment pattern136 a shown in FIG. 4A in accordance with some embodiments. In theexample shown in FIG. 4A, the alignment pattern 136 a is a square ring(i.e., a square with a central square hole inside), and the four cornersare round corners. Thus, the alignment pattern 136 a has a landing area402 surrounded by the alignment pattern 136 a. A target contact area 408a, located at the center of the landing area 402, is shown in the dashedline in FIG. 4A. In the example shown in FIG. 4B, the stabilizer landingfoot 138 a is aligned with the alignment pattern 136 a. That is, thecontact area between the stabilizer landing foot 138 a and the topsurface 404 of the bottom die 104 is within the landing area 402 a. Asmentioned above, the alignment between the stabilizer landing foot 138 aand the alignment pattern 136 a is being monitored in a real-time mannerusing the vision alignment camera 126 and the vision alignment processor172 shown in FIG. 1 in some embodiments.

FIG. 5 is a side view of an example bottom die 104 having alignmentpatterns 136 and stabilizer landing feet 138 in accordance with someembodiments. In the example shown in FIG. 5 , the alignment pattern 136can be located at position A. The alignment pattern 136 is located inthe bonding layer 156, and there is no semiconductor devices above orbelow the alignment pattern 136. The alignment pattern 136 is locatedoutside the seal ring 510 in the horizontal plane (i.e., the X-Y plane).The alignment pattern 136 is an optically recognizable pattern such thatit can be recognized by the vision alignment camera 126 of FIG. 1 . Insome implementations, the wavelength of the light being used is in thevisible light range (i.e., about 380 nm to about 700 nm). In otherimplementations, the wavelength of the light being used is outside thevisible light range. In one example, the wavelength of the light beingused is in the in the infrared (IR) range (i.e., about 780 nm to about 1mm). The alignment pattern 136 is made of a material having a refractiveindex or reflectivity different than that of the bonding layer 156. Inone example, the bonding layer 156 is made of a dielectric such as SiO2,SiC, SiN, SiON, and the like, and the alignment pattern 136 is made ofcopper.

As shown in the enlarged illustration of the region 502, the landingarea 402 can be made of one or more of the following materials: adielectric (e.g., SiO₂, SiC, SiN, SiON, etc.); a metal (e.g., Cu, W,etc.); a metal compound (e.g., TaN, TiN, etc.); an organic material(e.g., a polyamide, etc.); and a single element material (e.g., Si,etc.) that can be used in semiconductor processing. In oneimplementation, the landing area 402 is made of a dielectric (e.g.,SiO₂, SiC, SiN, SiON, etc.), which is cost-effective.

In another implementation, the alignment pattern 136 can be located atposition B. The alignment pattern 136 is located in the bonding layer156, and there are semiconductor devices above or below the alignmentpattern 136. In yet another implementation, the alignment pattern 136can be located at position C. The alignment pattern 136 is located atthe front side of the bottom die 104, instead of the bonding layer 156.The alignment pattern 136 at position C can be used for alignment whenthe bottom die 104 is flipped, that is, the front side is facingupwardly.

Also, existing features in the bottom die 104 may be employed asalignment patterns. In one implementation, the alignment pattern 136 islocated at position D and is a TSV 154. It should be understood thatthis example is not intended to be limiting and other features of thebottom die 104 that are visible-light observable may also be employed.In another implementation, the alignment pattern 136 is located atposition E and is a seal ring. It should be understood that this exampleis not intended to be limiting and other features of the bottom die 104that are IR observable may also be employed.

FIG. 6 is a top view of an example alignment pattern 136 b in accordancewith some embodiments. In the example shown in FIG. 6 , the alignmentpattern 136 b is identical to the alignment pattern 136 a shown in FIG.4A except that the pattern widths at different sides are unequal. Thealignment pattern 136 b has a landing area 402 b surrounded by thealignment pattern 136 b. The target contact area 408 b, located at thecenter of the landing area 402 b, is shown in the dashed line in FIG. 6.

FIG. 7 is a top view of an example alignment pattern 136 c in accordancewith some embodiments. In the example shown in FIG. 7 , the alignmentpattern 136 c is a circular ring. Thus, the alignment pattern 136 c hasa circular landing area 402 c surrounded by the alignment pattern 136 c.The target contact area 408 c, located at the center of the landing area402 c, is shown in the dashed line in FIG. 7 . It should be understoodthat in another embodiment, a portion of the example alignment pattern136 c (e.g., half of the circular ring, a circular arc, etc.) can beemployed.

FIG. 8 is a top view of an example alignment pattern 136 d in accordancewith some embodiments. In the example shown in FIG. 8 , the alignmentpattern 136 d is in a polygon shape and has a landing area 402 d in thesame polygon shape (but smaller) surrounded by the alignment pattern 136d. The target contact area 408 d, located at the center of the landingarea 402 d, is shown in the dashed line in FIG. 6 . It should beunderstood that any polygon shape (e.g., a hexagon shape, an octagonshape, an arbitrary polygon having seven sides, etc.) can be employed.

FIG. 9 is a top view of an example target contact area 408 e inaccordance with some embodiments. In the example shown in FIG. 9 ,existing features in a bottom die are employed as alignment patterns.Specifically, four bottom dies 104 a, 104 b, 104 c, and 104 d arelocated on a host wafer and have seal rings 510 a, 510 b, 510 c, and 510d, respectively. In the example shown in FIG. 9 , a target landing area408 e is chosen based on the locations of the seal rings 510 a, 510 b,510 c, and 510 d. It should be understood that the location of thetarget landing area 408 e is just an example, and other target landingareas may be chosen as well. In some implementations, the designer ofthe host wafer can specify the target landing area 408 e in advance. Inother implementations, the pick-and-place system 100 shown in FIG. 1 canchoose the location of the target landing area 408 e on the fly based onthe topology of the host wafer, if the target landing area 408 e has notbeen specified in advance. It should be understood that the exampleshown in FIG. 9 is not intended to be limiting and other features (e.g.,TSVs) of a bottom die may be employed as alignment patterns.

FIG. 10 is a top view of an example alignment pattern 136 f inaccordance with some embodiments. In the example shown in FIG. 10 , thealignment pattern 136 f is comprised of four alignment patterns 136 f-1,136 f-2, 136 f-3, and 136 f-4, which are identical to the alignmentpattern 136 a shown in FIG. 4A. In the example shown in FIG. 10 , atarget landing area 408 f is chosen at the center of the alignmentpattern 136 f. It should be understood that the location of the targetlanding area 408 f is just an example, and other target landing areasmay be chosen as well.

FIG. 11 is a diagram illustrating the functioning of an example opticsalignment system 128 in accordance with some embodiments. In the exampleshown in FIG. 11 , the top die 106 is to be placed on the bottom die 104at the target position. The bonding layers 156 will be in contact witheach other as the suction head 120 shown in FIG. 1 descends in theZ-direction, and the hybrid bonding metal pads 158 are supposed to bealigned in the X-Y plane. The sealing ring 510 of the top die 106extends vertically into the bonding layer 156. Some fine-tune alignmentpatterns 1108 are located in the bonding layer 156 of the bottom die104. In the example shown in FIG. 11 , the optics alignment system 128is located to the left of the top die 106 in the X-Y plane. The opticsalignment system 128 includes, among other things, a processor 1106, alight emitter 1102, and a light receiver 1104. In one example, the lightemitter 1102 is a laser and emits a light 1110 toward the seal ring 510.In one implementation, the light 1110 is an infrared light which is ableto penetrate the bonding layer 156 of the top die 106, while the sealring 510 and the fine-tune alignment patterns 1108 can reflect theinfrared light (i.e., “infrared observable”). It should be understoodthat although an infrared light is used as an example, it is notintended to be limiting, and other wavelength ranges can be employed ifappropriate. The light receiver 1104 then receives the light 1110 afterrefraction and reflection and generates a received signal. As theposition of the top die 106 changes relative to the bottom die 104, thereceived signal changes accordingly. The processor 1106 can determinethe position of the top die 106 based on the received signal. As such,the optics alignment system 128 monitors the position of the suctionhead based on the fine-tune alignment patterns 1108 located at thebottom die 104. It should be understood that, in other implementations,the processor 1106 can be implemented as the vision alignment processor172 or the control unit 170 shown in FIG. 1 , which is not located inthe optics alignment system 128 situated at the auxiliary region 124 ofthe suction head 120 shown in FIG. 1 .

FIG. 12 is a diagram illustrating the functioning of another exampleoptics alignment system in accordance with some embodiments. In theexample shown in FIG. 12 , the top die 106 is to be placed on the bottomdie 104 at the target position. The bonding layers 156 will be incontact with each other as the suction head 120 shown in FIG. 1 descendsin the Z-direction, and the hybrid bonding metal pads 158 are supposedto be aligned in the X-Y plane. The sealing ring 510 of the top die 106extends vertically into the bonding layer 156. Some fine-tune alignmentpatterns 1208 a and 1208 b are located in the bonding layers 156 of thebottom die 104 and the top die 106, respectively. In the example shownin FIG. 12 , the fine-tune alignment patterns 1208 a and 1208 b are bothdiffraction gating structures, each having periodic patterns. When thehybrid bonding metal pads 158 are aligned in the X-Y plane, thefine-tune alignment patterns 1208 a and 1208 b are supposed to bealigned in the X-Y plane as well. On the other hand, when the hybridbonding metal pads 158 are not aligned in the X-Y plane, as shown inFIG. 12 , the fine-tune alignment patterns 1208 a and 1208 b are notaligned in the X-Y plane with some offset. As a result, the light 1210 aemitted from a light emitter reflects as it meets the fine-tunealignment pattern 1208 b in the top die 106, whereas the light 1210 bemitted from the light emitter reflects as well as it meets thefine-tune alignment pattern 1208 a in the bottom die 104. Similarly, alight receiver then receives the light after diffraction and generates areceived signal. Therefore, the received signal changes accordingly asthe position of the top die 106 changes relative to the bottom die 104.As such, the optics alignment system 128 monitors the position of thesuction head based on the fine-tune alignment patterns 1208 a and 1208 blocated at the bottom die 104 and the top die 106, respectively. In someimplementations, a processor can determine the position of the top die106 based on the received signal. The processor can be implementedeither as the vision alignment processor 172 or the control unit 170shown in FIG. 1 , or as a separate processor located in the opticsalignment system 128 situated at the auxiliary region 124 of the suctionhead 120 shown in FIG. 1 .

It should be understood that although the examples shown in FIG. 11 andFIG. 12 are related to optics alignment systems based on reflection,refraction, or diffraction, they are not intended to be limiting. Inother implementations, the optics alignment system 128 shown in FIG. 1may be based on vision-assistant alignment. For example, the opticsalignment system 128 shown in FIG. 1 may include a vision alignmentcamera similar to the vision alignment camera 126 shown in FIG. 1 andrelies on the vision alignment processor 172 shown in FIG. 1 . Thevision alignment camera for the optics alignment system 128 may havebetter performance (e.g., higher resolution) than the vision alignmentcamera 126 as the alignment of the suction head 120 is fine-tuned.

FIG. 13 is a schematic diagram illustrating an example pick-and-placesystem 1300 in accordance with some embodiments. The pick-and-placesystem 1300 is identical to the pick-and-place system 100 shown in FIG.1 , except that the pick-and-place system 1300 has two suction heads 120a and 120 b, which can operate separately and simultaneously.Specifically, the suction head 120 a and the gantry 114 are connectedthrough the suction shaft 130 a, whereas the suction head 120 b and thegantry 114 are connected through the suction shaft 130 b. Two secondarydrive mechanisms 116 a and 116 b are located at the gantry 114 and candrive the suction head 120 a and the suction head 120 b in the verticaldirection and in the horizontal plane, separately.

In the example shown in FIG. 13 , the suction head 120 a places the topdie 106 a, which is a functional die, on the bottom die 104, whereas thesuction head 120 b places the top die 106 b, which is a dummy die, onthe bottom die 104. It should be understood that this is not intended tobe limiting. In other examples, both the top die 106 a and the top die106 b can be functional dies.

The suction head 120 a and the suction head 120 bb share the stabilizer118 while they can operate separately and simultaneously, thus achievinghigher operation efficiency and still keeping the stability provided bythe stabilizer 118.

Each of the suction shafts 130 a and 130 b is connected to a vacuumdevice. In other implementations, the suction shafts 130 a and 130 b areconnected to the same vacuum device. Also, each of the suction heads 120a and 120 b has its own optics alignment system to make sure that thetop dies 106 a and 106 b are placed at their target positions using thealignment feedback loop explained above with reference to FIG. 2 . Itshould be understood that although two suction heads are shown in FIG.13 , it is not intended to be limiting. In other embodiments, more thantwo suction heads can share the same stabilizer while operatingseparately and simultaneously.

In accordance with some aspects of the disclosure, a pick-and-placesystem is provided. The pick-and-place system includes: a wafer holderconfigured to hold a bottom die; a gantry having a stabilizer extendingdownwardly; a primary drive mechanism connected to the gantry andconfigured to drive the gantry horizontally and vertically; a suctionhead configured to hold a top die; and a secondary drive mechanismlocated at the gantry and connected to the suction head and configuredto drive the suction head horizontally and vertically to place the topdie on the bottom die at a target position. The primary drive mechanismdrives the gantry vertically until the stabilizer is in contact with thebottom die before the secondary drive mechanism drives the suction head.

In accordance with some aspects of the disclosure, a method foroperating a pick-and-place system is provided. The method includes:picking, by a suction head, a top die; driving, by a primary drivemechanism, a gantry connected to the primary drive mechanism above abottom die; driving, by the primary drive mechanism, the gantryvertically until a stabilizer extending downwardly from the gantry is incontact with the bottom die; and driving, by a secondary drive mechanismlocated at the gantry and connected to the suction head, the suctionhead horizontally and vertically to place the top die on the bottom dieat a target position.

In accordance with some aspects of the disclosure, a pick-and-placesystem is provided. The pick-and-place system includes: a wafer holderconfigured to hold a bottom die; a gantry having a stabilizer extendingdownwardly; a primary drive mechanism connected to the gantry andconfigured to drive the gantry horizontally and vertically; a firstsuction head configured to hold a first top die; a second suction headconfigured to hold a second top die; a first secondary drive mechanismlocated at the gantry and connected to the first suction head andconfigured to drive the first suction head horizontally and verticallyto place the first top die on the bottom die at a first target position;and a second secondary drive mechanism located at the gantry andconnected to the second suction head and configured to drive the secondsuction head horizontally and vertically to place the second top die onthe bottom die at a second target position. The primary drive mechanismdrives the gantry vertically until the stabilizer is in contact with thebottom die before the first secondary drive mechanism drives the firstsuction head and the second secondary drive mechanism drives the secondsuction head.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A pick-and-place system comprising: a waferholder configured to hold a bottom die; a gantry having a stabilizerextending downwardly; a primary drive mechanism connected to the gantryand configured to drive the gantry horizontally and vertically; asuction head configured to hold a top die; and a secondary drivemechanism located at the gantry and connected to the suction head andconfigured to drive the suction head horizontally and vertically toplace the top die on the bottom die at a target position; and whereinthe primary drive mechanism drives the gantry vertically until thestabilizer is in contact with the bottom die before the secondary drivemechanism drives the suction head.
 2. The pick-and-place system of claim1, wherein the stabilizer includes three or more legs extendingdownwardly from the gantry.
 3. The pick-and-place system of claim 2,wherein the three or more legs have three stabilizer landing feetrespectively, and the bottom die has three or more alignment patterns ona top surface of the bottom die corresponding to the three or more legs,respectively.
 4. The pick-and-place system of claim 3, wherein when thestabilizer is in contact with the bottom die, the three or morestabilizer landing feet are aligned with the three or more alignmentpatterns.
 5. The pick-and-place system of claim 3, wherein the top dieand the bottom die are bonded using hybrid bonding.
 6. Thepick-and-place system of claim 5, wherein a bonding layer of the bottomdie and a bonding layer of the top die are in contact, and the three ormore alignment patterns are located in the bonding layer of the bottomdie.
 7. The pick-and-place system of claim 3 further comprising: avision alignment camera located at the gantry configured to detect aposition of the gantry based on the three or more alignment patterns andassist the primary drive mechanism in aligning the three or morestabilizer landing feet with the three or more alignment patterns,respectively.
 8. The pick-and-place system of claim 1 furthercomprising: a vision alignment camera located at the gantry configuredto detect a position of the gantry to assist the primary drive mechanismin driving the gantry to a target gantry position.
 9. The pick-and-placesystem of claim 1 further comprising: an optics alignment system locatedat the suction head and configured to: monitor a position of the suctionhead; and generate an alignment feedback based on the position of thesuction head.
 10. The pick-and-place system of claim 9, wherein thesecondary drive mechanism drives the suction head based on the alignmentfeedback.
 11. The pick-and-place system of claim 9, wherein themonitoring is based on a fine-tune alignment pattern located at thebottom die.
 12. The pick-and-place system of claim 9, wherein themonitoring is based on fine-tune alignment patterns located at thebottom die and the top die.
 13. The pick-and-place system of claim 1,wherein the secondary drive mechanism has a higher movement resolutionthan the primary drive mechanism.
 14. A method for operating apick-and-place system comprising: picking, by a suction head, a top die;driving, by a primary drive mechanism, a gantry connected to the primarydrive mechanism above a bottom die; driving, by the primary drivemechanism, the gantry vertically until a stabilizer extending downwardlyfrom the gantry is in contact with the bottom die; and driving, by asecondary drive mechanism located at the gantry and connected to thesuction head, the suction head horizontally and vertically to place thetop die on the bottom die at a target position.
 15. The method of claim14, wherein the driving, by the primary drive mechanism, the gantryvertically until the stabilizer extending downwardly from the gantry isin contact with the bottom die comprises: driving, by the primary drivemechanism, the gantry vertically to a predetermined height at a firstspeed; and driving, by the primary drive mechanism, the gantryvertically at a second speed until the stabilizer extending downwardlyfrom the gantry is in contact with the bottom die, wherein the secondspeed is slower than the first speed.
 16. The method of claim 14,wherein the driving, by the secondary drive mechanism, the suction headhorizontally and vertically to place the top die on the bottom die atthe target position comprises: monitoring, by an optics alignmentsystem, a position of the suction head; generating an alignment feedbackbased on the position of the suction head; and driving, by the secondarydrive mechanism, the suction head based on the alignment feedback. 17.The method of claim 14, wherein the stabilizer includes three or morelegs extending downwardly from the gantry.
 18. The method of claim 17,wherein each of the three or more legs has a stabilizer landing foot,and the bottom die has three or more alignment patterns on a top surfaceof the bottom die corresponding to the three or more legs, respectively.19. A pick-and-place system comprising: a wafer holder configured tohold a bottom die; a gantry having a stabilizer extending downwardly; aprimary drive mechanism connected to the gantry and configured to drivethe gantry horizontally and vertically; a first suction head configuredto hold a first top die; a second suction head configured to hold asecond top die; a first secondary drive mechanism located at the gantryand connected to the first suction head and configured to drive thefirst suction head horizontally and vertically to place the first topdie on the bottom die at a first target position; and a second secondarydrive mechanism located at the gantry and connected to the secondsuction head and configured to drive the second suction headhorizontally and vertically to place the second top die on the bottomdie at a second target position; and wherein the primary drive mechanismdrives the gantry vertically until the stabilizer is in contact with thebottom die before the first secondary drive mechanism drives the firstsuction head and the second secondary drive mechanism drives the secondsuction head.
 20. The pick-and-place system of claim 19, wherein thefirst suction head and the second suction head operate separately andsimultaneously.